Pulsed Laser Processing Research Articles

Numerical study of multi-phase flow in ultrashort pulse laser processing

Ultrashort pulse laser processing is highly valued due to its enormous potential for high micromachining quality while it comprises complicated physical mechanisms especially when the pulse width falls in the regime about 10 ps. This study presents a complete mathematical modeling on multi-phase phenomena in ultrashort pulse laser processing, such as melting, vaporization, and solidification. The volume of fluid (VOF) technique is used to capture the interface during phase transition. Based on this hybrid model, the transport of energy and mass are investigated to study the influence of laser parameters on the formation of laser ablation hole. This work develops the incompressible multiphase laser ablation solver based on PIMPLE algorithm. The calculation results are validated by different references under different laser processing parameters which emphasize the importance of mechanism on thermal ablation and hydrodynamics in picosecond laser processing. More calculation results about the trends in hole depth over pulse laser width, laser fluence, and the number of pulses show the intricate influence of laser parameters.

Research on Textured Polishing Wheel (TPW) patterns for polishing dental ceramic materials in anhydrous environments

Abstract Dental ceramics commonly utilize high-hardness fused silica materials for the fabrication of inlays, crowns, and artificial dental implants, with their processing efficiency and surface roughness (Ra) directly influencing manufacturing costs and product quality. This study presents the development of a Textured Polishing Wheel (TPW) featuring three distinct surface patterns (spiral, linear, and radial), achieved through single-point diamond and pulsed laser processing techniques. It investigates the effects of these patterns on the removal rate and surface roughness (Ra) of dental ceramics during the polishing process. Results indicate that while TPW demonstrates comparable material removal depth to non-textured polishing wheels, it marginally increases surface roughness (Ra). Moreover, TPW significantly reduces burning and wear on the wheel surface during polishing. Pulsed laser ablation of TPW leads to further improvement in surface roughness, thereby enhancing the processing of dental ceramics. Experimental findings highlight the superior performance of spiral TPW, achieving a material removal rate of 4.2 μm/h and a surface roughness (Ra) of approximately 2.2 nm , thus meeting the manufacturing and functional requirements of dental ceramics.

Pulsed laser processed FeSiBCuNb glassy alloy with polyphasic nanostructure interactions for efficient degradation of reactive red 195 via photoactivating persulfate

An Fe73.5Si13.5B9Cu1Nb3 amorphous ribbon was used as a precursor to fabricate biphasic and polyphasic nanostructure catalysts via pulsed laser processing. The enhancement in nanostructure heterogeneity, light absorption ability, surface hydrophilicity and photothermal conversion of the catalyst resulted in improving photocatalytic performance, evidenced by a higher k value, increased total organic carbon removal rate, and lower ΔE value. The degradation pathway of reactive red 195 molecules in the persulfate system was proposed. Density-functional theory simulations indicated that the excellent catalytic performance of the pulsed laser catalyst was due to its unique polyphasic nanostructure, which induced the reduction in the energy barrier of the rate-determining step (from 2.74 to 1.34 eV) during the conversion of S2O82− to SO4−•. The processed catalyst exhibited an ultrahigh catalytic ability of kSA•C0 = 7733 mg·m−2·min−1 and strong reusability (28 cycles) without efficiency decay. This study revealed that regulating the nanostructure of the catalyst is an effective strategy to achieve high photocatalytic performance.

88‐2: The Characteristics Analysis for Laser Cutting Process of Multilayers Display Panels

In this study, we analyzed the laser cutting characteristics of pulse transverse electrical discharge in gas at atmospheric pressure (TEA) CO2 and ultraviolet (UV) pulse laser processing in a multilayer display panels. First, the numerical calculation for was performed to confirm the thermal characteristics of each materials and optical field distribution at the interface of different material layers. Also, processing characteristics were experimentally confirmed by measuring cutting profile and adhesion characteristics of layer interface. Experimental results show that the characteristics of multi layers polymer cutting have different trend from those in a single‐layer because of the optical and thermal properties of each layer. In particular, the interface of layers had a substantial affect due to optical field distributions and thermal characteristic difference. Also, the optical absorbance of layers affect adhesion at the interface. The result suggests proper processing condition to enhance the laser ablation processing quality of multilayer display panel. In conclusion, understanding the characteristics of multilayer laser cutting processing is important for determining the optimal conditions for display panel micromachining and enhancing the quality of laser cutting for the cutting edge technology.

High-Performance Bioinspired Hierarchical Microgroove Wick for Ceramic Vapor Chambers Achieved by Nanosecond Pulsed Lasers.

Directly integrating ceramic vapor chambers into the insulating substrate of semiconductor power devices is an effective approach to solve the problem of heat dissipation. Microgrooves that could be machined directly on the shell plate without contact thermal resistance and mechanical dislocation offer exciting opportunities to achieve high-performance ceramic vapor chambers. In this study, a bioinspired hierarchical microgroove wick (BHMW) containing low ribs via one-step nanosecond pulsed laser processing was developed, as inspired by the Sarracenia trichome. The superwicking behavior of microgrooves with different structural parameters was investigated using capillary rise tests and droplet-spreading experiments. The BHMW exhibited excellent capillary performance and anisotropic hemiwicking performance. At a laser scanning spacing of 30 μm, the BHMW achieved a capillary wicking height of 114 mm within 20 s. The optimized BHMW demonstrated a capillary parameter (ΔPc·K) and an anisotropic hemiwicking ratio of 4.46 × 10-7 N and 11.93, respectively, which were 1182 and 946% higher than references, as achieved through nanosecond pulsed laser texturing under identical parameters. This work not only develops a high-performance hierarchical alumina microgroove wick structure but also outlines design guidelines for high-performance ceramic vapor chambers for thermal management in semiconductor power devices.

Equivalent power densities model for multi-pulse ultrashort pulsed laser processing

Equivalent power densities model for multi-pulse ultrashort pulsed laser processing

Study on the Wettability and Abrasion Resistance of Ultrafast-Laser-Textured Ti Surface

Titanium (Ti) materials are highly valued in the medical field for their outstanding biocompatibility and corrosion resistance. However, challenges such as suboptimal wettability and wear resistance can impact the tribological properties of titanium implants, potentially leading to implant failure. This study explores the application of ultrafast pulsed laser processing to create two distinct structures, circular pits and grooves, on the surface of titanium materials. The samples underwent low-surface-energy treatment, after which the wettability and wear resistance of the textured surfaces were evaluated. The findings indicate that the textured surfaces exhibit improved hydrophobic properties and reduced surface wear. Specifically, the textured surfaces demonstrated a remarkable 73.68% reduction in wear compared to the untextured surfaces. These results underscore the potential of etching textured structures onto titanium surfaces to enhance their wear resistance, thereby offering promising implications for the improvement of titanium implant performance.

Pulsed laser-indued nanoscale phase transition in FePC alloy with enhancing the catalytic activity in dye wastewater degradation

A nanoscale heterogeneous environmental catalyst, FePC alloy, was successfully fabricated by a single-roller melt spinning technique. The prepared catalyst had a biphasic disorder structure with α-Fe nanocrystallites embedded in the amorphous matrix. The pulsed laser process effectively improved the nanoscale heterogeneity degree, thermodynamic properties, surface photothermal conversion, corrosion resistance and hydrophilicity of the catalyst. The 60 W pulsed laser processing induced the nanocrystalline Fe3P precipation in the catalyst, which is transformed from α-Fe and amorphous matrix, promoting the electron donation rate of the galvanic cell system; therefore, the 60 W pulsed laser processed catalyst exhibited an excellent catalytic performance, such as a high k value, strong TOC removal rate and low activation energy. In addition, compared with other oxide, metallic crystal and metallic glass catalysts, this catalyst exhibited a much higher surface area-normalized rate constant kSA. The reusability test showed that this catalyst exhibited a reliable stability, and its decolorization efficiency at the 20th cycle still remained above 95 %; moreover, the parameter analysis showed that it had a strong adaptability in the persulfate system. This study provides a new strategy for designing and fabricating the efficient, low-cost and environmental catalysts for dye wastewater degradation.

Reconstruction of laser-induced microstructures temperature profiles

Metallic microstructures are currently widely used in micro-optoelectronics, sensorics, microfluidics, and other applications. A promising direction in the creation of such microstructures is pulsed laser processing of thin metal films. To improve laser technologies and simulate ongoing processes, data on the temperature fields that arise during laser exposure are needed. The article shows that the temperature distribution on the surface of a material during pulsed laser heating can be obtained from optical, scanning electron or atomic force micrographs. The proposed approach opens up the possibility of estimating temperature fields from archival photographs of various microstructures.

Damage mechanisms of Ti3AlC2 ceramics in pulsed laser processing

The damage mechanisms of Ti3AlC2 ceramics during laser processing in air and water were studied using the pulsed laser. The focused high-energy laser induced the melting of surface of Ti3AlC2 ceramics, causing the decomposition of Ti3AlC2 into TiC and Al with Al rapidly evaporating. During the laser processing in the air, oxygen diffused inward to form a solid solution of TiCxOy, and the rapidly heating and cooling of resolidified layer generated high thermal tensile stresses to result in a large amount of microcracks. When processing in the water, the thermal stresses were greatly weakened, and the outward diffusion of Al steam resulted in the voids on the sample surface. Additionally, it is determined that after treating in the air and water, the residual flexural strengths of Ti3AlC2 ceramics could retain the high values of 292 MPa and 484 MPa, and the Weibull moduli were kept at 7.2 and 16.0, respectively, exhibiting the excellent damage tolerance and high reliability.

Fabrication of spatially-variable heterostructured CoCrFeMnNi high entropy alloy by laser processing

This study investigates the fabrication of spatially-variable heterostructured CoCrFeMnNi high entropy alloy (HEA) using pulsed laser processing. Two distinct fabrication approaches, involving single-(SP) and double-sided (DP) laser passes, were employed. Microstructural characterization through electron backscatter diffraction revealed significant differences. SP-HEA exhibited a spatially heterogeneous microstructure with coarse columnar grains, while DP-HEA displayed a sandwich-like structure with fine equiaxed recrystallized grains. Microhardness mapping demonstrated a gradient trend in SP-HEA, with the fusion zone exhibiting the lowest hardness and the base material the highest. In contrast, DP-HEA displayed an overall soft-hard-soft structure. Tensile testing revealed distinct mechanical responses, with DP-HEA exhibiting higher strength and ductility compared to SP-HEA. The improved performance of DP-HEA was attributed to a more uniform distribution of heterogeneity, minimizing mechanical interactions between soft and hard domains. Moreover, corrosion resistance was assessed, showing that DP-HEA outperformed SP-HEA and non-processed material, suggesting superior stability in corrosive environments. These findings highlight the profound influence of fabrication parameters on the microstructure and mechanical properties of spatially-variable heterostructured HEAs. The study contributes valuable insights for material design and applications based on CoCrFeMnNi high entropy alloys.

Self-Shielding of X-ray Emission from Ultrafast Laser Processing Due to Geometrical Changes of the Interaction Zone.

Materials processing with ultrashort laser pulses is one of the most important approaches when it comes to machining with very high accuracy. High pulse repetition rates and high average laser power can be used to attain high productivity. By tightly focusing the laser beam, the irradiances on the workpiece can exceed 1013 W/cm2, and thus cause usually unwanted X-ray emission. Pulsed laser processing of micro holes exhibits two typical features: a gradual increase in the irradiated surface within the hole and, with this, a decrease in the local irradiance. This and the shielding by the surrounding material diminishes the amount of ionizing radiation emitted from the process; therefore, both effects lead to a reduction in the potential X-ray exposure of an operator or any nearby person. The present study was performed to quantify this self-shielding of the X-ray emission from laser-drilled micro holes. Percussion drilling in standard air atmosphere was investigated using a laser with a wavelength of 800 nm a pulse duration of 1 ps, a repetition rate of 1 kHz, and with irradiances of up to 1.1·1014 W/cm. The X-ray emission was measured by means of a spectrometer. In addition to the experimental results, we present a model to predict the expected X-ray emission at different angles to the surface. These calculations are based on raytracing simulations to obtain the local irradiance, from which the local X-ray emission inside the holes can be calculated. It was found that the X-ray exposure measured in the surroundings strongly depends on the geometry of the hole and the measuring direction, as predicted by the theoretical model.

Benefits of Femtosecond Laser 40 MHz Burst Mode for Li-Ion Battery Electrode Structuring.

In Li-ion batteries, ion diffusion kinetics represent a limitation to combine high capacity and a fast charging rate. To bypass this, textured electrodes have been demonstrated to increase the active surface, decrease the material tortuosity and accelerate the electrolyte wetting. Amongst the structuring technologies, ultrashort pulse laser processing may represent the key option enabling, at the same time, high precision, negligible material deterioration and high throughput. Here, we report a study on the structuring of electrodes with both holes and grooves reaching the metallic collector. Electrochemical models emphasize the importance of hole and line dimensions for the performances of the cell. We demonstrate that we can control the hole and line width by adjusting the applied fluence and the repetition rate. In addition, results show that it is possible to drill 65 µm-deep and ~15 µm-wide holes in nearly 100 µs resulting in up to 10,000 holes/s. To further reduce the takt time, bursts of 40 MHz pulses were also investigated. We show that bursts can reduce the takt time by a factor that increases with the average power and the burst length. Moreover, at comparable fluence, we show that bursts can shorten the process more than theoretically expected.

Femtosecond Laser Direct Writing of Flexible Electronic Devices: A Mini Review.

By virtue of its narrow pulse width and high peak power, the femtosecond pulsed laser can achieve high-precision material modification, material additive or subtractive, and other forms of processing. With additional good material adaptability and process compatibility, femtosecond laser-induced application has achieved significant progress in flexible electronics in recent years. These advancements in the femtosecond laser fabrication of flexible electronic devices are comprehensively summarized here. This review first briefly introduces the physical mechanism and characteristics of the femtosecond laser fabrication of various electronic microdevices. It then focuses on effective methods of improving processing efficiency, resolution, and size. It further highlights the typical progress of applications, including flexible energy storage devices, nanogenerators, flexible sensors, and detectors, etc. Finally, it discusses the development tendency of ultrashort pulse laser processing. This review should facilitate the precision manufacturing of flexible electronics using a femtosecond laser.

Gradient-Pattern Micro-Grooved Wicks Fabricated by the Ultraviolet Nanosecond Laser Method and Their Enhanced Capillary Performance.

Capillary-gradient wicks can achieve fast or directional liquid transport, but they face fabrication challenges by traditional methods in terms of precise patterns. Laser processing is a potential solution due to its high pattern accuracy, but there are a few studies on laser-processed capillary-gradient wicks. In this paper, capillary step-gradient micro-grooved wicks (CSMWs) were fabricated by an ultraviolet nanosecond pulsed laser, and their capillary performance was studied experimentally. The CSMWs could be divided into three regions with a decreasing capillary radius. The equilibrium rising height of the CSMWs was enhanced by 124% compared to the non-gradient parallel wick. Different from the classical Lucas-Washburn model describing a uniform non-gradient wick, secondary capillary acceleration was observed in the negative gradient direction of the CSMWs. With the increase in laser power and the decrease in scanning speed, the capillary performance was promoted, and the optimal laser processing parameters were 4 W-10 mm/s. The laser-enhanced capillary performance was attributed to the improved hydrophilicity and reduced capillary radius, which resulted from the increased surface roughness, protrusion morphology, and deep-narrow V-shaped grooves induced by the high energy density of the laser. Our study demonstrates that ultraviolet pulsed laser processing is a highly efficient and low-cost method for fabricating high-performance capillary gradient wicks.

Highly efficient catalytic performance and self-renewing behavior of Fe-based glass induced by pulsed laser

FeSiB metallic glass using pulsed laser processing is proved to show excellent catalytic performance in wastewater treatment for the first time by decolorizing and mineralizing reactive red 195. Pulsed laser can effectively improve the thermodynamic properties, surface photothermal conversion and hydrophilicity of catalyst. Compared with homogeneous FeSiB catalyst, heterogeneity α-Fe/FeSiB exhibits a high k value, strong TOC removal rate and low activation energy. Theoretical calculations indicate that the excellent catalytic performance of heterogeneity catalyst is attributed to its unique nanoscale biphasic disorder structure, resulting the energy barrier of the rate-determining-steps of the conversion of S2O82− to SO4−• is reduced from 2.20 to 1.52 eV. The reusability test of heterogeneity catalyst also shows that the abnormal recovery phenomenon of decolorization efficiency at the 19th cycle owing to its unique self-renewing. This study reveals that a nanoscale biphasic disorder structure is a new strategy for obtaining high catalytic rate and durability.

Influence of Laser Process Factors on Laser‐Induced X‐Ray Emission in High‐Repetition Laser Processes

Lasers have established themselves as a versatile tool that generates innovations in a wide range of fields, from automotive to surface engineering, medical applications, etc. A current research field for lasers is surface texturing in biomimetic, which aims to mimic nature‐inspired functionalities and mechanisms, for example, to tailor and control wetting, adhesion/friction, or optical properties of technical surfaces. Therefore, ultrashort pulse lasers are often the right choice to alter surface structures at microscopic scale. Moreover, the ongoing trend toward high‐average power lasers reaching “kilowatt class” levels even for ultrashort pulse lasers seems to be beneficial to increase throughput of this powerful laser technology for industrial production. However, several recent studies are reported on harmful X‐ray emissions arising from high‐intense ultrashort laser pulses which must be considered as a secondary laser beam hazard in risk assessment. Shining light on this topic, this article reports on a set of experiments investigating X‐rays emission induced by ultrashort pulse laser processing of different laser‐pretreated stainless steel sheets. The X‐ray measurements show the effect of roughness and scan number on the laser‐induced X‐ray emission dose. In addition, the dependency of X‐ray emission on the scan direction relatively to the laser beam polarization state is discussed.

Effects of pulsed laser processing on structural evolution of diamonds - A molecular dynamics and experimental study

The pulsed laser processing has been used for machining ultrahard diamonds. However, structural evolutions, along with microscopic mechanisms, have hardly been clarified. In the present study, a molecular dynamics model for describing the pulsed laser processing of diamonds was developed, and the calculation results were verified through corresponding experiments, by using the typical nanosecond pulsed laser processing. At first, the temporal evolution of the temperature field was calculated, establishing the correlation between the temperature distribution and material ablation phenomena. Besides, intricacies of dislocation generation mechanism were elaborately explained, indicating that stress waves played prominent roles in formation and propagation of dislocations. In order to understand the phase transition phenomena, including the graphitization, vaporization and solidification, variations in coordination numbers based on calculations, together with Raman and XPS characterizations on diamond samples before and after laser processing, were examined and compared. Moreover, different effects of the pulsed laser processing on polycrystalline and monocrystalline diamonds were compared. It was found that the polycrystalline diamond shows lower rate of temperature fall and lower velocity of stress waves. This study provides valuable insights into the microscopic mechanisms governing pulsed laser processing of diamonds, thereby broadening the scope for optimizing laser machining processes.

Nanosecond Laser Fabrication of Novel Micro-/Nanostructured Metal Surfaces: A Dual-Functional Supersurface Combining Antireflectivity and Superhydrophobic Properties.

The research and applications in the field of micro/nano surface manufacturing are progressively shifting their focus toward multifunctional surfaces. In practical applications, objects often need to operate under demanding environmental conditions, and single-function surfaces have inherent limitations in terms of performance, adaptability, and longevity. In this paper, a micro-/nanolayered structural strategy with dual functions of ultrahigh antireflective properties and superhydrophobicity was created on the surface of titanium alloy by using nanosecond pulsed laser processing, and two structural modes of periodic honeycomb and lattice with controllable shapes were designed. In addition, the morphology and formation mechanism of multilevel micro-/nanostructures were investigated in depth, combining laser texturization and silanization of substrate microstructures. The effects of the micro-/nanostructured morphology on the reflection and wettability properties were evaluated with different pulse widths and lateral overlap index. This study also demonstrated that water droplets exhibit excellent bouncing and rolling behavior on superhydrophobic surfaces, further verifying the excellent hydrophobic properties of the prepared samples. Furthermore, in addressing the challenges of susceptibility to dust contamination and performance degradation in extreme environments associated with antireflective surfaces, a series of durability and mechanical stability tests were conducted on controllability periodic micro-/nanostructured surfaces. Successfully meeting this challenge will open up great potential and opportunities for significant improvements in equipment performance and stable operation under extreme operating conditions.

Numerical Simulation and Experimental Optimization of Pulse Laser Processing Carbon Fiber Reinforced Polymer Plate

Numerical Simulation and Experimental Optimization of Pulse Laser Processing Carbon Fiber Reinforced Polymer Plate